1. Field of the Invention
The present invention relates to a torque hinge mechanism used for coupling a main body with an open/close member which is moved to an opened position or a closed position, and an apparatus including such torque hinge mechanism, such as a portable type information processing system.
2. Description of Related Art
FIG. 1 shows a model of a friction plate type torque hinge mechanism. Apertures 3 and 5 are formed in a friction plate 2 and a friction plate 4, and a shaft 6 is fitted into the apertures 3 and 5. The friction plate type torque hinge mechanism utilizes a frictional resistance generated between the two friction plates 2 and 4 for operating as a mechanism which couples a main body with an open/close member to cause plural open/close movements of the member to be possible and to stably maintain the open/close member at any angle to the main body. The mechanism using the two friction plates has been widely used along with another type of hinge mechanism, such as a hinge mechanism using a combination of a cylindrical bearing and a shaft. The use of a lubricant between the two friction plates has also been widely used to realize a smooth rotation by reducing the frictional resistance and to reduce abrasion of the friction plates.
It is required in the torque hinge mechanism that a torque at a static condition, called a static torque, and a torque at the rotational operation, called a dynamic torque, should be maintained within a predetermined range, and these torques are not changed over tens of thousands of open/close operations. These torques, however, cannot be kept at a constant level. For example, during use over a large number of open/close operations, the torque increases due to the decrease of the lubricant. In addition, the torque decreases due to the increase of a space between the friction plates caused by the abrasion of the surfaces of the friction plates, resulting in a generation of an undesired sound and a break of the rotated parts, so that a maintenance service is required. Sometimes, the trouble of the torque hinge mechanism causes a change of a gap between two glass substrates, in which a liquid crystal layer is held, of a liquid crystal display device attached to the torque hinge mechanism, resulting in an irregular display image.
In the portable type electric/electronic apparatus, such as a video camera, a notebook type personal computer, miniaturization and high reliability are required. It has been required in the portable type information processing apparatus to use parts formed as small as possible in the torque hinge mechanism to increase the portability. Since a large number of parts of the torque hinge mechanism are assembled in a small space in the main body and the open/close member, it is impossible to replace only the torque hinge mechanism at its defect. Accordingly, the entire liquid crystal display device including the defective torque hinge mechanism must be replaced. For the above reasons, a torque hinge mechanism with high reliability is required.
FIGS. 2 and 3 show the friction plate used in the prior friction plate type torque hinge mechanism. A lubricant holding mechanism, which includes a small aperture 10 passing or penetrating through the friction plate 9, as shown in FIG. 2, cutout portions (not shown) and a wave shaped surface 12 of the friction plate 9, as shown in FIG. 3, have been frequently used to supply the lubricant to the friction surfaces over a long period of time. It has been difficult to keep the required constant torque over the life time of the product without maintenance service. The inventor of the present invention has found that the cause of the trouble is a shortage of the lubricant since the lubricant cannot be consistently and stably supplied and cannot be stably held during the use over a long period of time. The inventor has also found that the shortage of the lubricant remarkably occurs when a high pressure is applied to the surface of the portions generating the friction. Since these lubricant holding mechanisms lead to a surface opposing the friction surface through a path, such as the lubricant holding mechanism itself or the aperture receiving the shaft, the lubricant held in the lubricant holding mechanism is pushed out to the opposite surface through the path at the application of the high pressure to the surface of the portion generating the friction, whereby an amount of lubricant held in the lubricant holding mechanism is decreased, so that the lubricant cannot be stably supplied.
Japanese Published Unexamined Patent Application 10-26128 discloses a mechanism in which a reservoir of grease is provided by forming small apertures or cutout portions in a friction plate.
Japanese Published Unexamined Patent Application 9-41781 discloses a frictional lock type hinge mechanism without using grease in which a shaft is fitted into an inside surface of a bush, a plurality of grooves extend along an axis of the shaft or a plurality of sprinkled fine recesses are formed on an inner surface of the bush or an outer surface of the shaft.
Japanese Published Unexamined Utility Model Application 8-1404 discloses a tilt hinge for an office automation apparatus in which a lubricant is applied between a friction washer and a spring washer.
Japanese Published Unexamined Utility Model Applications 6-45110 and 6-45111 disclose a mechanism in which at least one of a friction plate and a washer is made of a sintered oilless metal or a resin, such as Teflon.